Chasing efficiency in green homes (photos)

BOSTON--Gear for making buildings greener was on display at this year's BuildingEnergy conference of the Northeast Sustainable Energy Association, which seemed to have a greater emphasis on energy efficiency this year.

Pictured here is the inside of a solar hot-water storage tank from Stiebel Eltron. With solar hot-water systems, solar panels or tubes heat a liquid that is pumped into a storage tank to heat water.

One way to cut electricity use from lighting and to enjoy the benefits of natural light is through a skylight. "Daylighting" systems such as this one from Velux are an improvement over flat skylights because they can pipe light through attics and into the rooms below. Some of them also use lenses to magnify light. Because of the efficiency benefits, daylight systems can get a tax credit for buyers after a purchase, according to Velux.

One route to home energy efficiency is to make houses as air-tight as possible and add a lot of insulation, even on the exterior of the building. This model shows how this technique can create a wall with a R-value, or insulating value, of 45, which is very high. Two layers of insulating foam are added to the plywood exterior and packed cellulose is put into the wall cavity. All penetrations, such as those for electrical outlets, are sealed up to prevent air leaks. Preferred Building Systems manufacturers pre-fab superinsulated homes.

An important component of solar installations are trackers, the structures that hold up solar electric panels and position the panels toward the sun during the course of the day. This system here from AllSun Trackers, which could be used in a residential home yard, includes an inverter to convert from direct current to household electrical current. In high winds, the system will flatten out and lock in place.

Infrared cameras, which detect heat, are increasingly being used by energy auditors as a way to find heat loss inside homes. Locating hot spots on an exterior, for example, will provide clues as to where conditioned air is leaking through holes in the building shell.

It's a new business but one that could develop as electric vehicles take to the streets--Aerovironment is one of a handful of companies that are making electric car charging stations for households. Cars such as the Chevy Volt and Nissan Leaf can be charged with existing household outlets. But upgrading to a higher-voltage charging station, which need to be installed by an electrician, will cut charging time roughly in half.

Solar-powered street light options are expanding and starting to be used. Street lights from SolarOne, which use an LED light, are already being used at the University of Georgia, Abu Dhabi, and a few other locations. Solar-powered street lights from another company, Sol, were donated as part of Haiti relief efforts.

LED lighting is a common feature of green-building conferences and increasingly are being touted as replacements for incandescent or compact florescent bulbs. These LED bulbs from LED Waves are designed for downlighting applications and general-purpose use. A 60-watt replacement bulb uses eight watts, according to a company representative.

Another common display at green-building conferences is a demonstration of the differences between different types of building insulation. In the past few years, sprayed-in foam insulation has come into favor because it not only insulates a wall cavity or attic, but also seals, which prevents conditioned air from leaking out. This display has air blow from below to show how air flows through fiberglass but much less through foam, allowing foam to retain more heat.

Green roofs are a way to insulate rooftops and reduce the amount of water run-off with plants. Typically, green roofs are used on flat commercial buildings.

Biomass is one form of renewable energy that is used widely but doesn't get as much attention as solar or wind. German manufacturer, Viessman, which makes solar hot water systems, now also makes biomass heating systems for industrial use. They can be run by burning wood chips, sawdust, or pellets.